Temperature-compensated carburetor choke control



March 23, 1965 J. F. GILBERT 3,174,687

TEMPERATURE-COMPENSATED CARBURETOR CHOKE CONTROL Filed June 21, 1962INVENTOR JOHN F. GILBERT 114, CAME w W BY ATTORNEYS United States Patent3,174,687 TEMPERATURE-COMPENSATEB CARBURETUR CHOKE (IGNTROL John F.Gilbert, 309 Broadway, Hazard, Ky. Filed June 21, 1962, Ser. No. 204,141Claims. (ill. 236-91) This invention relates to temperature-responsivedevices, and more particularly to mechanisms for controlling thecarburetor air inlet opening for an internal com bustion engine, inaccordance with the temperature of the engine and the ambient air.

Temperature responsive choke mechanisms for carburetors are well knownin the art and almost all of these devices have a bimetallic element asthe actuator. The bimetallic element is produced in the form of anelongated strip arranged as a helical coil. The inner end of the coil issecured to a rotating shaft upon which the butterfly valve, or choke, ismounted and the other end of the bimetallic element is attached to astop mechanism whose position may be adjustably fixed upon the body ofthe carburetor.

The bimetallic element is contained within a chamber through which airmay be drawn, which air has come in contact with a portion of the engineso that as the engine warms up, the rise in temperature Will becommunicated to the bimetallic element.

The construction of the helically wound bimetallic element is such thatas its temperature increases, the coil will tend to contract or wind-up,the effect of this Winding up being to open the butterfly valve topermit an increase in the amount of air 'fed to the mixing chamber ofthe carburetor.

One of the disadvantages of the conventional automatic choke mechanismsis that while they are extremely efifective so long as the weathertemperatures remain within a fairly constant range, diificulties arisewhenever there is a large drop in the temperature of the surroundingair. This lowering of the outside temperature (which tends to cause thebimetallic coil to unwind) tends to increase the pressure with which thechoke valve is urged in its closed position. The result of thisincreased pressure is that the temperature of the air introduced intothe chamber containing the helical coil may not be suiiicient tocompensate for this initial pressure to open the choke a suhicientamount, with the result that the gasoline and air mixture ted to theengine is excessively rich with gasoline.

In order to partially overcome the difiiculties with prior art devicesit is customary to change the setting of the fixed end of the bimetallicelement in accordance with the season of the year. This, of course, isan inconvenience to the motorist and so is not a solution to theproblem, but only a makeshift compromise with an impractical mechanism.

In order to overcome the diiiicul-ties enumerated above, it is thereforean object of this invention to provide a temperature compensated meanswhereby the angular movement of the valve mechanism will remain constantregardless of the temperature of the surrounding air.

It is also an object of the invention to provide means for use with acarburetor choke valve such that the force exerted by the valve againstits seat when in a closed position will remain the same irrespective ofthe am bient temperature.

It is another object of the invention to provide automaticchoke-operating mechanisms for internal combustion engine carburetorswhich when initially set in an adjusted position will not requirefurther adjustment in response to seasonal chan es in the range oftemperatures of the atmosphere.

Other objects and advantages will become apparent antes? Patented Mar.23, 1965 "ice to those skilled in the art after reading the followingspecification in connection with the annexed drawings, in which:

. FIG. '1 is a side elevation of one form of temperaturecompensatedcarburetor choke control made in accordance the teachings of thisinvention with a portion of the carburetor housing included;

FIG. 2 is an end elevation of the device shown in FIG. 1 as observedfrom the right-hand side;

FIG. 3 is an end elevation as observed from the left side as shown inFIG. 1;

FIG. 4 is a cross sectional elevation taken on the line 4-4 of FIG. 3;and

FIG. 5 is a perspective View of a helical bimetallic coil strip.

Referring now to the drawings in detail, the choke control mechanismgenerally is indicated by the numeral 19 and is shown as being attachedto that portion of the housing 11 which usually forms the chamberthrough which air heated by the engine exhaust manifold is drawn toactuate the conventional automatic choke control; it being understoodthat the provision of such a chamber in a carburetor and the method andmeans of supplying such heated air to the chamber, are well known in theart and form no part of the present invention.

Preferably, the control means of the present invention is containedwithin a cup-shaped housing 12 having an end wall 13. The open end ofthe cup-shaped housing is closed by a circular plate 14 which may beprovided with a radially extending flange 15, adapted to be receivedwithin a recessed seat 16, usually provided at the open end of thecarburetor housing 11.

The inner face of the end wall 13 is provided with a centrally locatedsocket 17 containing a bushing 18 for rotatably receiving one end of ashaft l9. The plate 14 is also provided with a centrally located opening29 to re ceive the bushing 21 in alignment with the bushing 1'3 toadditionally support the shaft ll? medially of its ends. The bushing 21is annularly recessed as at 22 to receive a resilient O-ring seal 23 toprevent leakage of air from one side of the plate 14 to the other sidethrough the shaft opening.

The inner periphery of the open end of the housing 12 may be annularlyrecessed as at 24 to assist in positioning the housing on the carburetorhousing 11 and to enable the housing as a whole to be rotated about theaxis of the shaft 19. The end Wall 13 may also be annularly recessed asat 25 to receive the clamping ring 26 which is, itself, secured to thecarburetor housing 11 by a plurality of bolts 27 received Withinthreaded openings 28 which are usually provided about the periphery ofthe opening in the carburetor housing.

In the conventional carburetor having an automatic choke, the portion ofthe housing indicated by the numeral 11 is closed by a cover, which inthis invention is replaced by the plate 14 to provide a closed chamberindicated by the numeral 29, through which chamber, as previouslystated, air is circulated after being brought into contact with, andheated by, a portion of the manifold of the engine.

One of the ends of the shaft 19 extends into the chamber 29 and isprovided with an axially extending diametrically cut slot 30, withinwhich is received the flattened inner end 31 of a helically coiledbimetallic strip 32.. The outer end of this bimetallic strip is providedwith an outwardly projecting leg 33 which bears against the actua ingarm 34 of a butterfly valve numeral 45 placed in the air inlet of thecarburetor 46. Bimetallic strips of this type are well known in the artand have the characteristic that it the inner portion 31 of the strip isheld in a fixed position, the outer leg 33 will move angularly about theaxis of the coil 32. in one direction or the other in response tochanges in the temperature of the coil. In common practice, the coiltends to unwind (or to move the leg 33 in a clockwise direction asviewed in FIG. 5) when subjected to a decrease in temperature. However,it will be understood that the principles of operation of this inventionwould be equally applicable if the reverse were the case.

The other end of the shaft 19 is also axially slotted at 35 to receivethe flat inner end 31 of a bimetallic coil strip 32' which has the samephysical and mechanical characteristics as the metallic coil 32. Theprojecting leg 33 may be set in a slot in a fixed anchor 36 attached tothe inner face of the end wall 13. Between the coil 32 and the bushing21, the shaft 19* is provided with an annularly projecting shoulder 37.An L-shaped stoplever 38, which may be fabricated of sheet metal, isprovided with an opening 39 to enable the arm to be pressfitted on theshaft 19 against the shoulder 37 and thus held fixedly with respect tothe shaft. The other endof the stop-lever may bear against one side ofan adjustable stop member 40 which is received Within a circular slot 41provided in the end wall 13 and having its axis of curvature coaxialwith the shaft 19.

In understanding the operation of the invention, it should be realizedthat the purpose of a temperature-compensated choke mechanism is tocontrol the admission of air to the carburetor only during the initialoperation of the engine, it being necessary to reduce the proportion ofair when the engine is cold and to gradually increase the proportion ofair as it warms up. Once the engine has reached its normal operatingtemperature, the choke valve should be completely open and there shouldbe no reduction in the air intake regardless of the speed or load underwhich the engine is operating.

It should also be understood that after an internal combustion enginehas been out of operation for a certain length of time, it becomescooled to the temperature of the surrounding air circulating over itsexposed surfaces. Therefore, prior to the starting of an engine, thebimetallic coiled strip 32 will be at approximately the same temperatureas the bimetallic strip 32', regardless of the fact that the strip 32 iscontained within a closed chamber, while the strip 32' is in more directcontact with ambient air through slot 41 in the end plate.

Further, it should be understood that the elements 32 and 32' arearranged on the shaft 19 so that the resultant angular movement of oneof the elements is neutralized by the resultant angular movement 'of theother element. This is accomplished by placing the respective coils 32and 32' on the shaft 19 so that the direction of rotation of theconvolutions of both helical coils is in the same direction. It can beseen in FIG. 2 that the coil 32 spirals outwardly from the center in acounterclockwise direction, and therefore the coil 32' should also bearranged so that it spirals outwardly from the center when viewed fromthe rear end of the shaft. Conversely, when viewed from the front of thehousing (as in FIG. 3) both coils 32 and 32' would be observed asspiraling outwardly from the shaft in a clockwise direction.

The result of such an arrangement is as follows: so long as the engineis not operating, a temperature drop of the surrounding air will affectboth of the bimetallic elements to cause both coils to tend to unwind onthe shaft. As viewed from the front of the housing, this unwinding ofcoil 32 will turn'shaft 19 angularly a certain amount in a clockwisedirection, since the leg 33 is fixed to anchor 36. If the shaft 19 wereconnected to the actuating arm 34 of the choke valve, the effect of theunwinding of coil 32' would be to tend to move the arm 34 with theshaft. However, since the arm 34 is connected with the shaft 19 by thebimetallic coil 32, and, since it is the inner end 31 of the coil 32that is anchored to the shaft, the resultant unwinding of the coil 32will be a counterclockwise rotation of the leg 33 with respect; to theshaft and, because the characteristics of the two coils are identical,the counterclockwise angular movel ment of the leg 33 with respect tothe shaft will be equal and opposite to the clockwise angular rotationof the shaft by the coil 31'. There is thus no change in the angularposition of the leg 33 with respect to the housing 11 and no change inthe effects exerted against the arm 34.

If there is a subsequent rise in the ambient temperature, so long as theengine is not running, the shaft 19 will be rotated by cell 32' in acounterclockwise direction in accordance with the temperature change;but there will be a corresponding winding of coil 32 which will nullifythe rotation of the shaft to maintain the same force against theactuating arm 34.

To install the temperature-compensated actuating mechanism, the completeassembly with the cover 14 covering the open end of the cup-shapedhousing 12 and the coiled strip 32 in place at the end of shaft 19, isinserted in place at the open end of the housing 11 with the protrudingleg 33 angularly spaced to the right of the choke actuating arm 34, asviewed from the outer end in FIG. 3; the housing 12 is then rotated in acounterclockwise direction until the leg portion 33.contacts the arm 34and this rotation is continued until the choke valve is closed andplaced under slight tension by the combined effect of a slight windingforce applied to spring 32 and the equal and opposite unwinding forceapplied to coiled strip 32'. The end plate of the cup-shaped housing maybe provided with boss 43 provided with a diametrically extending slot 44adapted to receive the blade of a screwdriver or other similar tool toassist in rotating the housing. With the housing in this position, theclamping ring 26 is applied and tightened on the. outer end of the housing by the bolts 27. To complete the adjustment, the stop member in theslot 41 is wound in a clockwise direction until it is placed in contactwith the downwardly projecting end of the stop-lever 38, and theadjusting a screw 42 is tightened to hold the stop member 40 in thisposition.

These adjustments having been made, no further adjustment will benecessary regardless of seasonal changes in temperature. When the engineis started, the air circulating in the chamber 29, as previouslyexplained, will begin to warm up in response to an increase in thetemperature of the engine manifold. As the air in this chamber increasesin temperature, the bimetallic coil 32 which is exposed to this air,will tend to wind up. However, since the bimetallic coil 32' is exposedto the temperature of the ambient air only, there will be no change inthe angular position of the shaft 19. But, since the shaft 19 doesremain in the same position, the wind-up of the element 32 causesangular movement of the leg portion 33 in a clockwise direction,together with choke valve arm 34. This clockwise movement continuesuntil the air in the chamber 29 having reached its operatingtemperature, the clockwise movement of the leg 33 and arm 34- has beensufiicient to completely open the choke butterfly valve- When the engineis stopped, the drop in temperature of the air in the chamber willgradually cause the bimetallic strip 32 to unwind in a counterclockwisedirection until the choke is again closed.

During the initial period of warming up of the engine, the bimetallicelement 32 will be substantially unaffected by the presence of heatedair in chamber 29 due to the presence of the O-ring seal 23 surroundingthe shaft 19, and to the fact that the heat transferred by conductionthrough the shaft and the housings l1 and 1.2, will not appreciablyaffect the element 32' until after the warm-up period has beencompleted. During continued operation of the engine, the temperature ofthe element 32 will normally become elevated due to heat transfer byconduction and also because of the possibility that the air in theimmediate vicinity of the carburetor which enters through the slot 41will have its temperature elevated. Since an increase in the temperatureof element 32' would tend to cause it to wind up, the effect of thiswould be to rotate the shaft in a counterclockwise direction. At thispoint, the air in chamber 29 having reached its operating temperature,there would be no further change in the condition of the element 32,thus, the counterclockwise rotation of the shaft by the element 32'would cause bodily rotation of the element 32 in addition causing theleg 33 to move in a counterclockwise direction and urging the chokelever 34 towards its closed position. Since this is an undesirablecondition, once the engine has reached operating temperature, the stopmember 40 prevents such counterclockwise movement of shaft 19 bylimiting coun terclockwise rotation of the stop-lever 38. t will thus beseen that the stop member 46 will permit any amount of clockwiserotation of the shaft 19 induced by the unwinding of the bimetallicelement 32' in response to dropping temperatures, but will limitcounterclockwise rotation of the shaft (tending to close the chokevalve) which may be induced by increases in the ambient air to which theelement 32' may become exposed.

In the claims, it should be understood that the phrase enginetemperature refers to the temperature of the air circulated in thechamber 29 or to any medium employed to affect changes in the bimetallicelement 32 as a function of the operating temperature of the internalcombustion engine with which the carburetor is associated. The phraseambient air is intended to refer to the temperature of the air in theenvironment in which the internal combustion engine and its associatedmechanisms are being operated.

Having disclosed one form in which the invention may be practiced itwill be understood that modifications and improvements may be made whichwould come within the scope of the annexed claims.

I claim:

1. In temperature-compensated carburetor choke control mechanisms forinternal combustion engines having a valve actuated by an arm rotatableabout a fixed axis in one direction from a closed position to aplurality of open positions, the combination including, a shaft mountedfor rotation about an axis concentric with said fixed axis, firsttemperature-responsive means connected between said shaft and said armto move said arm in said one direction With respect to a given angularposition of said shaft With increases in an engine temperature, secondtemperatureresponsive means connected with said shaft to rotate saidshaft in a direction opposite to said one direction in response todecreases in ambient temperature, and enclosure means in communicationwith air heated by an internal combustion engine surrounding one of saidtemperature-responsive means for heat-exchanging relationship betweensaid one temperature-responsive means and an engine, said othertemperature-responsive means being exposed to ambient air.

2. The invention as defined in claim 1, wherein stop means is providedto limit movement of said shaft in said opposite direction.

3. The invention as defined in claim 1, wherein both saidtemperature-responsive means comprises substantially identical helicalbimetallic strips.

4. The invention as defined in claim 1, wherein a casing having a walldisposed normal to the axis of said shaft is provided, said shaft havinga radially extending member fixed thereto, said end wall being providedwith an arcuate slot concentric with said shaft axis, and an elementslidable in said slot to limit movement of said radial member in onedirection at a plurality of predetermined positions.

5. A device of the character described for attachment to internalcombustion engine carburetors provided with temperature-responsive chokemeans, said choke means including a chamber in communication with airheated by an engine and having a circular opening and a bimetallichelical element mounted on an axis concentric with said circular openingto regulate a choke control arm, the combination including, a generallycup-shaped casing having its open end adapted for adjustably rotatableengagement with the circular opening in a carburetor chamber, platemeans to isolate the interior of the cup-shaped casing from a carburetorchamber, a shaft, said cup-shaped casing having a bushing forconcentrically rotatably supporting one end of the shaft Within thecasing, concentrically positioned sealed bushing means in said platemeans for rotatably supporting said shaft with the other end projectinginto a carburetor chamber, means at said other end of the shaft tosupport the central end of a bimetallic helical element, a secondbimetallic helical element similar to said first helical element, meansto support the central end of the second bimetallic element at the oneend of the shaft, and means to connect to outer end of the secondbimetallic element to the cup-shaped casing said casing being incommunication with ambient air.

6. The invention as defined in claim 5, wherein adjustable stop means isprovided to limit rotation of said shaft in one direction.

7. The invention as defined in claim 6, wherein said stop means includesa radially projecting element on said shaft, and an arcuately movablemember adjustably fixed on said casing.

8. In temperature-compensated choke control mechanisms for carburetorsfor internal combustion engines of the character whereintemperature-responsive means is provided tending to exert force to closethe air inlet of a carburetor in response to decrease in enginetemperature and to open said inlet in response to increase in enginetemperature, the combination including, second temperature-responsivemeans in communication with ambient air, means to isolate said secondtemperature-responsive means from heat-exchanging relationship with anengine, and means to connect said second temperature-responsive meanswith said air inlet to exert an equal and opposite force on said firsttemperature-responsive means in response to changes in ambient airtemperature when an engine is inoperative.

9. In automatic controls for internal combustion engine carburetorshaving a choke valve means movable in one direction to a closedposition, yieldable temperature-influenced compound actuating means forsaid choke valve means, said compound actuating means including firstand second temperature-responsive mechanisms, means for placing one ofsaid mechanisms in communication only with an engines air, and means forplacing the other mechanism in communication only with ambient air, saidactuating means being adjustable in a plurality of positions to exert apredetermined force on said choke valve means in closed position when anengine is inoperative, said predetermined closing force beinguninfluenced by changes in ambient air temperature.

10. The invention as defined in claim 9, wherein means is provided tosubject said compound actuating means to both ambient air temperatureand engine temperature, said actuating means being responsive toincrease in engine temperature due to operation thereof to relieve saidclosing force on said choke valve means and to progressively open saidvalve means.

References Cited by the Examiner UNITED STATES PATENTS 2,043,834 6/36Marbury 73363.1 X 2,145,230 1/39 Arrighi 236101 2,939,445 6/60 Sterner261-392 FOREIGN PATENTS 135,591 11/33 Austria.

EDWARD 1. MICHAEL, Primary Examiner.

FREDERICK L. MATTESON, IR., Examiner.

9. IN AUTOMATIC CONTROLS FOR INTERNAL COMBUSTION ENGINE CARBURETORSHAVING A CHOKE VALVE MEANS MOVABLE IN ONE DIRECTION TO A CLOSEDPOSITION, YIELDABLE TEMPERATURE-INFLUENCED COMPOUND ACTUATING MEANS FORSAID CHOKE VALVE MEANS, SAID COMPOUND ACTUATING MEANS INCLUDING FIRSTAND SECOND TEMPERATURE-RESPONSIVE MECHANISMS, MEANS FOR PLACING ONE OFSAID MECHANISMS IN COMMUNICATION ONLY WITH AN ENGINE''S AIR, AND MEANSFOR PLACING THE OTHER MECHANISM IN COMMUNICATION ONLY WITH AMBIENT AIR,SAID